He added: “while the utilitarian value of nature is important conservation goes beyond this. Do these species have a right to survive or do we have a right to drive them to extinction?”

“All the species listed are unique and irreplaceable. If they vanish, no amount of money can bring them back. However, if we take immediate action we can give them a fighting chance for survival. But this requires society to support the moral and ethical position that all species have an inherent right to exist,” said Dr Ellen Butcher of the Zoological Society of London, a co-author of the report.

Their declines have mainly been caused by humans, but in almost all cases scientists believe their extinction can still be avoided if conservation efforts are specifically focused. Conservation actions deliver results with many species such as Przewalski’s Horse, Equus ferus, and Humpback Whale, Megaptera novaeangliae, have being saved from extinction.

The 100 species, from 48 different countries are first in line to disappear completely if nothing is done to protect them.

The pygmy three-toed sloth, Bradypus pygmaeus, is one of the animals facing a bleak future. Escudo Island, 17km off the coast of Panama, is the only place in the world where these tiny sloths are found. At half the size of their mainland cousins, and weighing roughly the same as a newborn baby, pygmy sloths are the smallest and slowest sloths in the world and remain Critically Endangered.

Similarly, the saola, Pseudoryx nghetinhensis, is one of the most threatened mammals in Southeast Asia. Known as the Asian unicorn because of its rarity, the population of these antelope may be down to few tens of individuals today.

In the UK, a small area in Wales is the only place in the world where the brightly colored willow blister, Cryptomyces maximus, is found. Populations of the spore-shooting fungi are currently in decline, and a single catastrophic event could cause their total destruction.

“If we believe these species are priceless it is time for the conservation community, government and industry to step up to the plate and show future generations that we value all life,” Prof Baillie said.

“Whilst monetizing nature remains a worthwhile necessity for conservationists, the wider value of species on the brink of extinction should not be disregarded.”

“All species have a value to nature and thus in turn to humans,” said Dr Simon Stuart, Chair IUCN Species Survival Commission. “Although the value of some species may not appear obvious at first, all species in fact contribute in their way to the healthy functioning of the planet.”